Speaking with the many suppliers of flowmeters and other instrumentation while researching “The Consumer Guide…” book series led to the interesting observation that almost all suppliers claim to sell the best equipment. Therefore, finding the best equipment can be a challenge. Unless these suppliers sell equipment that performs identically (which the research shows is not the case), equipment from these suppliers cannot all be the best. In contrast, a few suppliers will admit that their equipment is not the best, but is adequate for many applications. It is also interesting to note that the price of the best equipment is often competitive with the price of average and below average equipment.
Which of the following are logical approaches to determining the quality of an instrument?
A. Evaluate the supplier’s verbal statements.
B. Obtain and test instruments from different manufacturers. Compare the test results.
C. Compare equipment specifications.
D. Determine the operating parameters for the application. Calculate performance at the operating flow rates.
There is some value to all of the answers. In Answer A, the salesperson’s statements should provide a broad filter that may be used to determine the potential usefulness of the instrument in the application. This should be done with the understanding that there are financial incentives for each supplier to claim to supply superior equipment, so their statements may be somewhat optimistic.
Obtaining and testing equipment of different manufacture (Answer B) is perhaps the best approach for determining the quality of an instrument. It gives the user hands-on experience with the instrument and independent test data. However, with some instruments (including flowmeters) this can be so costly and labor intensive that only the largest companies can afford it.
Comparing instrument specifications (Answer C) relies on supplier claims that describe instrument performance. Understand that accuracy statements can be manipulated because some suppliers’ specifications push the limits while other suppliers are more conservative. While this approach may not be able to discern whether an instrument ranks 43rd or 44th out of 60 instruments (who cares anyway?), the information gathered can generally find the 3-5 instruments that should be seriously considered for purchase.
Answer D could be considered a subset of Answer C and it also relies on supplier claims. The performance of some instruments varies with full scale flow rate. For example, the accuracy of a magnetic flowmeter model may be identical for a wide range of flow rates in many sizes. In contrast, the accuracy of a given size and model Coriolis flowmeter varies with flow rate. Supplier specifications can be used to calculate the performance of these flowmeters at various operating flow rates. The results can be compared to determine which flowmeter would perform better in this application.
Additional Complicating Factors
Instrument specifications are usually complete, but at times can be complicated. In addition, they are often expressed in a manner that makes the instrument appear to perform better than other instruments by emphasizing the portion of the specification that puts their instrument in a positive light. Caveats and constraints are often located in the fine print. The user is advised to be sure that performance calculations include all portions of the specifications.